Sizing the snowpack

January 5, 2018

Every day, the Natural Resource Conservation Service, a division of the U.S. Department of Agriculture, gathers statistics about water levels and snowpack. These tell a great deal not only about what’s on the ground now but also about what to expect in months to come.

I’ve checked these numbers at least weekly for years (they’re posted online at https://wrcc.dri.edu/snotelanom/snotelbasin) and they’ve offered a fair indication, when you put them into context, for what’s coming by way of water supply in areas all over the western United States.

This year, Idaho is coming off a good water year, and that should help the state at least somewhat in maintaining an adequate water supply in months to come. The year before that, 2016, conditions were dryer, but in most places still better than in much of the west, where drought was prevalent. In a number of other recent past years, the state has seen drought.

So, three months or so into the new water year (annualized measurements start in October), what does 2018 look like?

The set of stats I check most closely are those showing the “percentage of normal accumulated precipitation,” which very roughly translates to: How good is the snowpack, at this point, compared to historical averages? Those numbers vary around the state, and they’re broken out by river basins, or in some cases other regions.

To get a sense of what they mean (get ready for some numbers), you can compare them with past years at the same time. Here’s how some of the basins look as of now.

• In the northern Panhandle, the current percentage is 103. Last year at this time it was 134, and in 2016 it was 120.

• The Salmon River basin now reports 90 percent. In 2017, it was 106; the year before, 115.

• The Payette basin is coming in at 82 percent. A year ago, it reported 99 percent; in 2016, it was 115.

• The Boise now shows 79 percent. Last year this time: 104 percent; the year prior, 120.

• The Big Wood is clocking in at 79 percent too. In 2017: 124 percent. In 2016: 118 percent.

• The Bear River now is at 76 percent. Last year it showed 137 percent; the year before, 86 percent.

• The Snake River above Palisades Dam is at 97 percent of the norm. In 2017, it was 155 percent; in 2016, 92 percent.

You can catch a few themes in this.

One is that a really good water year (in a particular place) can help tide over an area receiving less the next. (The Bear River area would be an example.)

But you also can see how the accumulation levels this year overall are a good deal shallower than they were last year, or the year before. They’re also, on balance, a little lower than in 2015. (And note too: They’re lower still to Idaho’s southwest and south.)

The last year they were lower – and then they were significantly lower – was in 2014, though in that year the state happened to pick up enough snow and rain in late winter to help out, and the snowpack returned to roughly normal levels. But you could consider that a late save.

Get ready for some careful water usage and conservation, and extra caution in the wildfire department, in the months to come.